I'm watching the DVD now. Pug Henry was not at the Polish-German front. That was his younger son Byron. Captain Henry did visit the Russian-German front a few hours outside of Moscow. To answer your question, I suppose it is possible that someone in the diplomatic service could have managed to meet Churchill, Hitler, Mussolini, and Stalin, visit the Russian front, and hitch a ride on that air raid, but there would have been a trail littered by a gaudy volume of memoirs. Enjoy this for what it is, over-the-top-storytelling at its best.
I did some digging Pug Henry was very loosely based upon a more jr rank officer who nearly did everything henry did--
Example for the meeting with Churchill and stalin--he was assigned to different officers who were at meetings--as for if he was in the room--that is where no one is quiet sure. If I find the (I think) London Times article I will post. The actual jr rank office was of German/English Heritage who knew four languages and was in his early 20's (no kids or wives), he died in a plane crash in the late 40's early 50's.